Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.49   9.619%   $268.0075   $268.01   $268.00   $268.00  
  Purchase #2 $186.75   7.654%   $201.0438   $201.04   $201.05   $201.00  
  Purchase #3 $27.49   4.351%   $28.6861   $28.69   $28.70   $28.70  
  Purchase #4 $202.79   7.422%   $217.8411   $217.84   $217.85   $217.80  
  Purchase #5 $115.71   12.204%   $129.8312   $129.83   $129.85   $129.80  
  Purchase #6 $234.90   4.677%   $245.8863   $245.89   $245.90   $245.90  
  Purchase #7 $148.94   6.755%   $159.0009   $159.00   $159.00   $159.00  
  7 purchase totals = $1,161.07       $1,250.2969   $1,250.30   $1,250.35   $1,250.20